1. Field of the Invention
The present invention relates to a magnetic course detector, wherein the bearing of the course of a traveling body, especially for example an automobile, is detected by detecting the direction of the terrestrial magnetism by means of a magnetic bearing sensor mounted in the traveling body, characterized in that the bearing of the course of the traveling body is accurately detected by regulating the offset and sensitivity of the output of the abovementioned magnetic bearing sensor as well as rotatably mounting the same.
2. Description of the Prior Art
It has hitherto been contrived to detect the bearing of the course of a traveling body by detecting the direction of the terrestrial magnetism using a magnetic bearing sensor detecting the direction of the magnetic field, such as shown in FIG. 1 (A). In what is called a flux-gate magnetic bearing sensor 1 shown in FIG. 1 (A), an exciter coil 3 wound on a ring core 2 is supplied an alternating current of frequency f in order to excite the ring core 2 so that it is repeatedly saturated and unsaturated. In this state, if a magnetic field (terrestrial magnetism in this case) having a magnetic field intensity He is applied as shown in FIG. 1 (A), higher harmonics of frequency 2f and proportional to the magnetic field intensity He are generated in detection coils 4a, 4b crossing each other at right angles, and detection circuits 5a, 5b generate positive and negative DC voltages V.sub.X, V.sub.Y proportional to the magnetic field intensity He. The generated voltages or the outputs V.sub.X and V.sub.Y of the abovementioned magnetic bearing sensor 1 are the X-axis and Y-axis components of the terrestrial magnetism vector He respectively, and they are given by the formulas: ##EQU1## where K is a constant of proportionality. Then, if the magnetic bearing sensor 1 is rotated 360.degree. with respect to the direction of the terrestrial magnetism, the locus obtained by the outputs V.sub.X and V.sub.Y of the magnetic bearing sensor 1 is a circle l.sub.1, as shown in FIG. 1 (B), given by the formula: EQU V.sub.X.sup.2 +V.sub.Y.sup.2 =(KHe).sup.2 =a.sup.2 ( 2)
Accordingly, the direction of the terrestrial magnetism, or a magnetic north, can be obtained by means of the outputs V.sub.X and V.sub.Y of the magnetic bearing sensor 1. Thus, if, the Y-axis direction, for example, of the magnetic bearing sensor 1 is made to coincide with the course of the traveling body, the bearing of the course of the traveling body with respect to magnetic north can be known.
When the above-mentioned magnetic bearing sensor 1 is mounted in a vehicle formed from iron plates such as an automobile, however, the X-Y outputs of the magnetic bearing sensor 1 may be offset due to residual magnetism in the iron plates or the like forming the vehicle due to magnetization of these parts when assembling the vehicle. In other words, the origin O of the X-Y outputs of the magnetic bearing sensor 1 is shifted to the point O' shown in FIG. 2 by the residual magnetism vector, represented by arrow Hr. As a result, the locus of the outputs (V.sub.X, V.sub.Y) of the magnetic bearing sensor 1 on the basis of the terrestrial magnetism vector He is such as l.sub.2 shown in FIG. 2. Consequently, even though the direction of the terrestrial magnetism vector He is the direction of an arrow O'P in the Figure, the bearing vector obtained by the outputs of the magnetic bearing sensor 1 becomes a composite vector (vector OP in FIG. 2) of the abovementioned residual magnetism vector Hr and the terrestrial magnetism vector He, and so it is impossible to accurately detect the direction of the terrestrial magnetism.
In addition, even if a correction is made for the effects of the abovementioned residual magnetism, the anisotropy of magnetic permeability, i.e. how easy it is for magnetic flux to pass, attributable to the configuration of a vehicle with an iron-plate structure, results in the intensity of the terrestrial magnetism differs according to the direction of incidence of the terrestrial magnetism. Consequently, the output values of the magnetic bearing sensor 1 vary, so that normal outputs cannot be obtained. In other words, as shown in FIGS. 3 (A), (B), a vehicle 6 such as an automobile has a generally rectangular plan, so that it is easy for magnetic flux 7 to pass through the vehicle 6 in its longitudinal direction as shown in FIG. 3 (A) but difficult in its lateral direction as shown in FIG. 3 (B). Accordingly, when the magnetic bearing sensor 1 is mounted in the vehicle 6 so that the Y direction of the magnetic bearing sensor 1 coincides with the longitudinal direction or the traveling direction of the vehicle 6 as shown in the Figure, the locus of the outputs obtained from the magnetic bearing sensor 1 is not a correct circle, and it is experimentally known that the locus of the outputs of the magnetic bearing sensor 1 obtained when the vehicle 6 turns 360.degree. with respect to the direction of the terrestrial magnetism is an ellipse with a major axis in the Y direction, such as l.sub.3 shown in FIG. 3 (C). In other words, because the detection sensitivity in the X direction of the magnetic bearing sensor 1 is low, it is impossible to accurately detect the magnetic bearing without suitable improvements.
Moreover, depending on the position the magnetic bearing sensor 1 is installed in the vehicle 6, the aforementioned magnetic permeability differs, so that the effect of the anisotropy thereof becomes complicated. For example, when the magnetic bearing sensor 1 is installed in the right rear corner of the vehicle 6 as shown in FIG. 4, it is easiest for the magnetic flux 7 to pass the vehicle 6 when crossing it from the left rearward to the right frontward as shown in FIG. 4 (B), while it is most difficult for the magnetic flux 7 to pass the vehicle 6 when it is turned 90.degree. counterclockwise from the state shown in FIG. 4 (B), as shown in FIG. 4 (C). From the above, when the magnetic bearing sensor 1 is positioned in the vehicle 6 as shown in FIG. 4, the locus of the outputs of the magnetic bearing sensor 1 obtained when the vehicle 6 turns 360.degree. with respect to the direction of terrestrial magnetism (the direction of the magnetic flux 7) is an ellipse like l.sub.4 shown in FIG. 5. In other words, as described above, because the state shown in FIG. 4 (B) where the magnetic flux 7 passes most easily is the case where the course of the vehicle 6 is counterclockwise offset from the direction of the magnetic flux 7 by an angle .theta., a locus such as the ellipse l.sub.4 is obtained, whose major axis is clockwise inclined at an angle .theta. with respect to the Y axis. Accordingly, when the position of the magnetic bearing sensor 1 is installed in the vehicle is asymmetric with respect to the vehicle as shown in FIG. 4, for example, it is impossible to accurately detect the magnetic bearing without a suitable improvement.